1. Field of the Invention
This invention relates to novel catalytic compositions and their use as reforming catalysts. More specifically, these catalysts comprise the joint use of zeolites with conventional reforming catalysts such as platinum or platinum-rhenium or multi-metallics on alumina.
2. Description of the Prior Art
Catalytic reforming of naphtha feed stocks has long been known in the petroleum industry. Most naphtha feeds contain large amounts of naphthenes and paraffins and consequently have low octane numbers. By means of various hydrocarbon conversion reactions, catalytic reforming has improved the octane number of naphtha feed stocks. Some of the more important conversion reactions that take place during catalytic reforming are dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to naphthenes and aromatics and isomerization of normal paraffins to isoparaffins. A less desirable reaction that also occurs during reforming is the hydrocracking of long chain paraffins to gaseous hydrocarbons such as methane and ethane.
The above reforming reactions have previously been catalyzed by catalysts comprising porous supports, such as alumina, that have dehydrogenation promoting metal components impregnated or admixed with the support. Platinum on alumina and, more recently, multimetallics, including bimetallics, such as platinum and rhenium on alumina, are examples of these catalysts.
Reforming catalysts should possess high selectivity, high activity and good stability. Selectivity in reforming is the ability of a catalyst to selectively produce high yield of high octane products, such as aromatics, from compounds that have relatively low octane numbers, such as naphthenes and paraffins. The activity of a catalyst is the ability to convert the feed stock into all products without regard to selectivity. A stable catalyst is highly desirable so that the activity and selectivity characteristics of a catalyst can be maintained during prolonged periods of operation.
It is known in the art to admix certain zeolites with other catalytic materials. For instance, British Pat. No. 1,056,493 discloses mixing together an alumina-supported platinum catalyst and a chabazite zeolite and using it in a hydrocracking operation. British Pat. No. 1,255,544 discloses a dual purpose catalyst comprising a zeolite, especially mordenite, having incorporated therein both platinum and rhenium. However, these patents do not suggest the catalysts of this invention since they do not afford the same advantages. The octane number improvement and their remarkable ability to withstand aging with the catalysts of this invention are significantly greater than can be obtained with the catalysts of the British patents mentioned.
U.S. Pat. No. 3,267,022 and U.S. Pat. No. 3,324,047 disclose composites of a zeolite having a pore size of from 6-14A and an adjuvant such as alumina. Hydrogenation activity is said to be imparted by adding, for example, a Group VIII metal, either to the zeolite or to the adjuvant. The amount of zeolite is from 20-80% by weight.
U.S. Pat. No. 3,544,451 refers to a hydrocarbon conversion catalyst which comprises platinum and rhenium combined with a carrier material containing alumina and finely divided mordenite. As will be shown hereinafter, combinations similar to those of the patent are ineffective for the purposes of the present invention.
U.S. Pat. No. 3,702,886 discloses a composite of from 1-90% of a zeolite, such as ZSM-5, with a matrix material and a hydrogenation component. The matrix materials include generally metal oxides, but not specifically alumina.
As another example of the state of the art, U.S. Pat. No. 3,758,402 discloses the hydrocracking of hydrocarbons to motor fuel products by contacting a hydrocarbon charge with acatalytic mixture containing hydrogenation components, a large pore size zeolite such as zeolite X or Y and a smaller pore size zeolite such as ZSM-5 and a matrix material, an example of which is alumina. The zeolite components may comprise from 1-95% of the final composite.
U.S. 3,365,392 discloses the catalytic reforming of gasoline charge stock to produce high octane reformate and LPG by contacting a charge with a catalyst comprising a platinum group metal on a support comprising a finely divided crystalline aluminosilicate suspended in an alumina matrix. The preferred aluminosilicate is the hydrogen or polyvalent form of mordenite, especially the hydrogen form thereof.
U.S. Pat. No. 3,546,102 is concerned with a hydrocarbon conversion catalyst consisting essentially of a co-catalytic support and a Group VIII metal. The support contains an adsorbent refractory inorganic oxide and mordenite structure zeolite. The preferred metal is platinum, and it is incorporated into the zeolite-inorganic oxide blend after blending but before drying and calcining.
Other U.S. patents disclosing catalytic composites comprising platinum, or rhenium, or both, optionally a matrix and mordenite as the sole or preferred cyrstalline aluminosilicate are U.S. Pat. Nos. 3,369,997, 3,376,214, 3,376,215, 3,464,929, 3,511,773, 3,523,914, 3,562,108 and 3,574,092.
All of the U.S. patents mentioned, can be distinguished on one or both of two different grounds. The first, already mentioned in connection with U.S. Pat. No. 3,544,451, is that it is conclusively shown herein that mordenite composites are inferior. The second is that no patent mentioned teaches or even suggests the extraordinary stability at high liquid yields at high octane numbers of the composites of this invention by controlling the activity so that its activity function will fall within the limits to be hereinafter defined.